Polymers have long been the most prevalent material used for forming yarns for use in the carpet industry. In recent years, polyester has become a desirable polymer for use in carpet fiber.
Carpets made from polyester, particularly polyethylene terephthalate, are superior in terms of acid dye stain resistance, an important attribute, and they generally do well in terms of texture retention (durability) and soil resistance compared to the other low cost alternative, polyolefin (e.g. polypropylene). However, carpets made from polyester, particularly polyethylene terephthalate, perform quite poorly in terms of texture retention (durability) and soil resistance compared to polyamides, including nylon 66 and nylon 6, and wool. As a result, applications for polyester fibers in carpeting are often limited to those channels in which the poor durability and accelerated soiling attributes are minimized, for example in a low foot traffic residential environment. However, in high traffic environments, such as commercial office buildings, airports and schools, polyester fibers have not been considered durable enough for flooring installations. The negative aspects of polyester fiber performance in carpeting applications is, however, offset by the attractiveness of the price of polyester, which is typically favorable as a raw material due to the high supply volume of polyester raw materials.
There is, therefore, a need to improve the performance of polyester fibers for carpet applications that overcomes its durability and soiling deficiencies. The combination of polyamide and polyester resins has been contemplated to either reduce cost (of polyamide) or to improve the final carpet fiber properties (of polyester). However, the relative immiscibility of the polyester and polyamide resins chosen can create difficulty in forming conjugate fibers. Blends comprising immiscible polymers have two or more phases, and such blends may be incompatible. Incompatible blends of immiscible polymers can suffer from phase separation and fibers formed from such blends may fibrillate, which would not provide the durability necessary for commercial use. Additionally, polymers from the same class are frequently immiscible and form multiphasic compositions. Therefore, polymer miscibility is difficult to predict, even within the same class of polymers.
For this reason, previous attempts at using a combination of polyester and polyamides in carpet have required the use of a compatibilizing agent or an additional component. U.S. Pat. No. 6,780,941 to Studholme, herein incorporated by reference, teaches blending of thermoplastic polyester with fiber-forming polyamide in the production of melt-spun fibers, wherein the polyamide component forms the major phase. In order to form the fiber, the use of at least 1% by weight or more of a metal sulfonated poly(butylene terephthalate) as a compatibilizing additive is required.
PCT Publication No. 2013133640, herein incorporated by reference, teach that due to a lack of compatibility, it is difficult to melt extrude fibers from polyester and polyamides. To solve this problem, the addition of a compatibilizing agent, such as an epoxy resin is required to form a usable alloy fiber. In addition, this publication only teaches fibers with a polyamide major phase and an effective compatibilizer loading at 2% by weight or more.
U.S. Pat. No. 6,090,494 teaches fibers that contain both polyamide and polyester filaments. However, to be effective and avoid fibrillation, the amount of polyester is limited and only fibers containing predominantly polyamide filaments are disclosed.
European Patent Application No. 2,748,259A1 teaches a composition comprising both polyamide and polyester components, wherein the polyester component is preferred at 40% or less by weight, and without requiring a compatibilizer. However, the disclosure does not teach a composition that can be effectively melt spun into a fiber.